Security does not simply mean building a wall or barring Syrian refugees.

This week’s deadly terror attacks in Brussels moved national security, and specifically border security, front and center in the presidential election.

This renewed focus is welcome, but it has been nearly 12 years since my colleagues and I on the 9/11 Commission’s border security team wrote a 233-page report, separate from the commission’s main findings, detailing how and why terrorists move around the world, exploit immigration laws and weak border controls for destructive ends — and how they can be detected and disrupted.

That we are still having the same conversation about what to do to fix our broken borders all these years later clearly indicates that, whatever might have been done to improve border security, it has not been enough.

As we recommended in 2004, we must make border security an integral part of U.S. national security; we must focus immigration regulation and law enforcement on preventing terrorist entry and embedding; and we must act internationally to make border, travel and immigration security a global priority.

Transnational terrorist groups need to travel to commit their acts of terror. They require freedom of movement for many reasons, including training, communications, surveillance, committing terrorist acts and escaping capture. Al-Qaeda understood the importance of travel with their ability to carry out attacks. They studied national immigration policies and practices, monitored modes of transportation and ports of entry, and trained operatives in the use of fraudulent travel documents and how to appear inconspicuous.

Therefore, when we speak of border security, it is important to be clear about what we mean. It does not simply mean building a wall on the southern border with Mexico or barring Syrian refugees. It starts with issuing secure identity and travel documents, progresses to issuing visas and proceeds to the port of entry. This also includes programs and benefits that allow non-citizens to remain in the country for extended periods. We must prevent terrorist exploitation at each of these stages. And, as the recent attacks in Brussels, Ankara and Paris make clear, in today’s interconnected world, so must our allies.

Every time terrorists engage a country's security apparatus — to cross a border or apply for a visa, for example — it’s an opportunity to detect, disrupt and apprehend. In fact, our team concluded that 15 of the 19 Sept. 11 hijackers were potentially vulnerable to interception.

Why weren’t they caught? The answer is because too many of our border security and immigration laws, policies and standard operating procedures, including what information is shared with front-line border security personnel, effectively conspired against it — and still do today.

We are still issuing multiple-year, multiple-entry tourist visas to citizens of high-risk countries, including Saudi Arabia (five years), Pakistan (five years) and Turkey (10 years), which shares a border with Iraq and Syria and is a major transit hub for ISIL. These visas allow travelers to apply for admission into the USA as many times as they’d like for the duration of the visa. This is important because as the 9/11 attack illustrates, this type of visa allowed the four pilots to come in and out of the U.S. 17 times over 21 months. (As an aside, all surviving visa applications, of which there were 19, were incomplete.)

We are still holding a “diversity” lottery in which we offer 50,000 green cards a year to citizens of "underrepresented” countries. We do not screen the applicants for critical skills or knowledge; it is literally a lottery: If your number is called, you win.

We still have not secured the southern border, nor have we reined in abuse of the immigration system, which, as my team detailed in our report, has historically been exploited by terrorists to plan and carry out attacks. The latest example of this exploitation can be found in the San Bernardino strike in which one of the perpetrators gained entry to the U.S. by marrying an American, something terrorists have been doing for decades.

Equally concerning are reliable reports suggesting as many as 5,000 European Union citizens traveled to Iraq and Syria to join ISIL. EU member states participate in the U.S. Visa Waiver Program (VWP), meaning that anyone with a Belgian passport, for example, can travel visa-free to the U.S., despite weak new rules imposed in January intended to stop terrorists.

One of the conditions for inclusion in the VWP is “maintenance of high counterterrorism, law enforcement, border control, and document security standards.” The recent European migration crisis, the attacks in Paris and Brussels, and an EU report calling for urgent improvements to border security raise serious questions about whether this standard is being met in all participating countries.

What is required now is not only a renewed focus and robust effort to urgently secure our nation’s border and enhance border security globally, but also new leadership to get the job done once and for all.

Kelly Moore worked with the State Department’s Counterterrorism Team and the United Nations in Croatia, Bosnia and Kosovo. Moore was also a member of the 9/11 Commission’s border security team.